Flotable sheet material has been used in the art for covering swimming pools so that during the cooler part of the swimming season, the floatable sheet material will retain the heat in the swimming pool water and, additionally, allow the water to be heated by sunlight. These covers are normally made of a translucent plastic which has been rendered buoyant so that the covers float on the swimming pool water but will allow the sun's rays to pass through the covers and heat the water in the pool. During cooler periods, these covers prevent loss of heat from the water in the swimming pools. The covers are not normally secured to the sides of the pool, but are originally manufactured, or cut, to substantially cover the water in the pool. When the pool is to be used, the covers are removed, often by rolling onto a reel system near the pool, and are again replaced on the pool when the pool is not in use.
The pool covers experience substantial stress when being removed from the pool or replaced thereon. Not only are the covers often of considerable size, and hence weight, e.g. 20 ft..times.40 ft., but especially when removing the covers from the pool, the covers will be wet and will entrain some water, thereby increasing the weight. Thus, the covers can be quite heavy, and correspondingly substantial strain is placed on the covers when removing from or placing on the pool. In addition, strong winds can move the covers about the pool, since they are free floating on the water, and that wind action can place additional stress on the covers.
As can be therefore appreciated, the covers must be strong and be able to withstand considerable stress, or otherwise the covers will deteriorate with use and begin to tear. Once the covers tear, they are, of course, more difficult to remove and replace on the pool and the stress during such removal and replacement increases the likelihood of causing greater tears.
Such pool covers may be made by a variety of methods, but by far most of the pool covers are made by attaching sections of floatable on water (buoyant), translucent laminated plastic sheet material. This sheet material is produced by laminating an embossed film with a plurality of embossments dispersed thereon to a backing film whereby air containing buoyant cells are formed by the embossments of the embossed film and the backing film. The laminated sheet material is usually made in widths of about 4 or 6 feet, and in continuous running lengths. The edges of the continuous running lengths (the longitudinal edges) are not embossed and do not, therefore, contain the buoyant cells. The running lengths of the sheet material are cut to appropriate lengths for a particular pool length and the width of the pool cover is achieved by attaching, one to the other, the appropriately cut running lengths. For example, for a 20 ft. wide and 40 ft. long pool cover, 4 feet wide running lengths are cut to sections of approximately 40 feet in length, and five of these 4 feet wide sections are attached, edge to edge, in order to provide the required 20 foot width of the pool cover.
The edges are attached, one to the other, by a variety of methods, but unfortunately all of these methods weaken the edges at the points of attachment. For example, when the edges are attached, one to the other, by heat sealing, that heat sealing weakens the attached edges. In addition heat sealing distorts the films and the pool cover will not lie flat on the water, resulting in an unsightly appearance. Similarly, when the edges are attached by adhesives or the like, the adhesives will likewise weaken and distort those attached edges, since an adhesive, in order to be effective, must in part dissolve the plastic of the sheet material. The strongest means of attachment of the edges are by sewing, but here again, the needle punctures of the edges during the sewing operation weakens the attached edges.
Thus, generally speaking, the weakest points of the pool cover are along the attachments of the edges of the sheet material. With continued use of the pool cover, as explained above, these weakest points begin to give way and the pool cover will tear and become unserviceable.
It would therefore be of substantial advantage to the art to provide such sheet material, where sections of the sheet material can be attached, edge to edge, without substantially weakening the attached sheets of materials at the attachments thereof. Correspondingly, it would be of decided advantage to the art to provide pool covers where the attachments of the sheet material do not substantially weaken the sheet material at the attachments thereof. Finally, it would also be a substantial advantage to the art to provide methods for producing such improved sheet materials and pool covers.